It is desired to reduce the amount of carbon dioxide emitted in an effort to reduce air pollution and slow down global warming. The automobile industry has introduced electric-powered cars (hereinafter “EV”) and hybrid cars (hereinafter “HEV”) to reduce the amount of the carbon dioxide emission, attracting considerable attention. Motor-driving secondary batteries are key to the practical application of these vehicles, and their development is now being actively pursued.
Non-aqueous electrolyte cells (also known as non-aqueous solvent-type secondary cells), in particular, lithium ion secondary cells, have the highest theoretical energy among all types of cells and have attracted much attention as motor-driving secondary cells. As such, their development is now being accelerated.
A typical lithium ion secondary cell includes a layered structure (power-generating element) including a positive electrode, a negative electrode, and an electrolyte layer connecting the positive electrode to the negative electrode. The power-generating element is usually packaged with a metal-resin laminate sheet constituted from a lightweight metal foil such as an aluminum foil and resin sheets laminated on both surfaces of the foil so that the electrode terminals project externally.
As for the collectors of the lithium ion secondary cell electrodes, a metal foil such as an aluminum foil is usually used as a positive electrode collector and a metal foil such as a copper foil is usually used as a negative electrode collector, for example.
Japanese Unexamined Patent Application Publication No. 2003-243038 discloses a lithium ion secondary battery in which, in the event of internal short circuit, the aluminum thin film is heated by the short circuit current flowing in the shorted part and the aluminum atoms diffuse to allow recovery of insulation in the shorted part to thereby prevent the temperature of the cell from increasing. However, when two or more cells are connected in series to form a battery and a short circuit occurs between the cells, the flow of the short circuit current continues even after insulation is recovered in the shorted part of the positive electrode. The cell temperature elevates as a result, and the cell may undergo breakdown.